1. Technical Field
This disclosure relates to water treatment in general and to methods of controlling hydrogen sulfide in aquatic and marine environments. The methods are useful for application to aquatic or marine animal ponds and sediments in need of treatment to control, minimize and/or eliminate hydrogen sulfide (H2S) to promote the yield and/or quality of aquatic and marine animals.
2. Background
Many aquatic and marine environments such as fish farms, pools, ponds, waste lagoons, lakes, estuaries, and oceans contain one or more aerobic zones and one or more anaerobic zones in the water column. In aerobic zones near the surface of the water column, air and winds introduce oxygen and aerobic bacteria produce, inter alia, phosphates, carbon dioxide and ammonia. In anaerobic zones near the bottom of the water column, anaerobic microorganisms tend to generate, inter alia, hydrogen sulfide, ammonia, and methane. Hydrogen sulfide accumulations in the anaerobic zones and sediments below are toxic and undesirable for they stress the aquatic and marine animal populations. In some cases, such as commercial fish and shrimp ponds, where populations live on or near the bottom of the water body in or near the anaerobic zone, the accumulation of hydrogen sulfide decreases the yield of the population and/or quality of individuals thereof.
There are several approaches to problems associated with the anaerobic zones known in the art. For example, chemical oxidizers, such as ozone, chlorine dioxide, and hydrogen, calcium, or magnesium peroxide, may be added to the water body to alleviate the anaerobic conditions. Although these methods may be effective, they may be expensive, pressuring users to minimize the amount of oxidizers added to the water body. The need to economize can be detrimental if it leads to under dosing. Under dosing is problematic in that it can cause incomplete or partial oxidation, creating odor problems. When chlorine dioxide is added to organic acids, incomplete oxidation can cause the formation of chloroacetic acid, which has a foul odor noticeable at very low concentrations. However, these steps are designed to eliminate odor and may be detrimental to the aquatic and marine animals in the environment such as shrimp or fish.
Other known methods for controlling hydrogen sulfide include treating water with oxygen. For example, U.S. Pat. No. 5,876,990 describes a biochemical media system for reducing pollution. The system includes a first media which provides an oxygen inducer to dissipate slowly into aqueous surroundings, and a second media which provides an oxygen supplier. The two media are combined in aqueous environment to generate nascent oxygen at a modulated rate such that the oxygen is absorbed into the surrounding aqueous environment, promoting growth of aerobic species and reducing biological pollution. However, the use of such a system does not necessarily alter the hydrogen sulfite concentration in the sediment below the water column and may also be detrimental to the aquatic and marine animals in the environment. Moreover, the cost of such a treatment may well outweigh the potential economic benefit of this for fish or shrimp farming.
Of interest is U.S. Pat. No. 7,160,712 (herein incorporated by reference in its entirety) which relates to methods for treating odors in wastewater treatment bodies. Here, odor problems are treated by altering the water chemistry to make the reduction of sulfur chemical species thermodynamically unfavorable, and bacteria, such as Paracoccus pantotrophus are added to the water. However, there is no suggestion to use such methods for improving the yield and/or quality of aquatic and marine animals such as in commercial fish farms.
Other methods of reducing hydrogen sulfide levels in a contaminated aquaculture include partial water exchange. However flushing methods may be impractical, expensive, and potentially dangerous if flush water introduces contaminants such as viruses and/or disease.
While chemicals and water flushing may be effective against hydrogen sulfide, these measures are expensive and may lead to a reduced yield and/or quality of aquatic or marine animals grown therein. It is thus desirable to have an effective, more problem free, biological or biochemical system that controls hydrogen sulfide accumulations in aquatic or marine environments and sediments thereof.